Many pointer-based interfaces allow selection of a particular item from among a large number of options, for example, a digital music player can allow a listener to select a particular song from within a catalog of thousands of songs. In another example, in the context of a military command and control center, an operator interface may allow selection of a particular asset (for tasking) from a large pool of available assets.
Forcing the user to perform the selection directly can be tedious and time consuming when a large number of choices is available. Consequently, many such interfaces ease the selection by providing a multi-step process. For example, a digital music player may allow a listener to designate a song by traversing a selection hierarchy (e.g. Artist:Album:Song). An operator interface in the command and control center may allow successive application of (not necessarily hierarchical) filters (e.g. NorthAmerica:Aircraft:Stealth) to narrow the range of available choices prior to final designation of an asset. At each step in the multi-step selection process, the interface requires the user to choose from among a manageable number of choices.
Completion of such a multi-step selection process with a pointer-based interface may remain difficult in unsteady or high stress environments. For example, a listener may struggle to select a song on a touch screen interface while walking or jogging, and the command and control center operator may struggle to accurately move a mouse or trackball in a crisis situation.